1. Field of the Invention
The present invention relates to a liquid crystal display device comprising a liquid crystal display element and a backlight. Particularly, the present invention relates to a liquid crystal display device that makes a color filter structure and a reflection film structure appropriate.
2. Description of Related Art
In recent years, semi-transmission type liquid crystal display devices capable of employing both a backlight and outside light have been developed.
The semi-transmission type liquid crystal display device has the advantages of being thin, light in weight, and low in power consumption.
The semi-transmission type liquid crystal display device comprises a liquid crystal display element and a backlight arranged behind the liquid crystal display element.
The semi-transmission type liquid crystal display device is provided with a semi-transmission film that reflects a part of light.
The semi-transmission film is formed by sputtering a metal film composed of aluminum or the like on a substrate and etching a light transmission region for each pixel, and performs a function of reflection display (a reflection mode) by a region where the metal film exists, while performing a function of transmission display (a transmission mode) in a region where no metal film exists.
In the reflection mode, outside light incident from a display surface passes a color filter two times, so that coloring (spectral transformation of light) by the color filter is increased, resulting in great loss of the outside light. Therefore, brightness in the reflection mode cannot, in some cases, be sufficiently obtained.
A region, corresponding to the reflection mode, in the color filter is provided with a hole of the color filter in a predetermined area so that the brightness of reflected light is improved.
According to the semi-transmission type liquid crystal display device, it is possible to obtain an image quality having high color purity in the transmission mode, while obtaining an image quality having a high reflection factor in the reflection mode.
On the other hand, as the disadvantage of the semi-transmission type liquid crystal display device, it is difficult to simultaneously satisfy the high color purity and the high reflection factor in the reflection mode.
FIG. 16 shows the relationship between the reflection factor and the color purity (the NTSC (National Television Standards Committee) ratio) of a liquid crystal panel in a case where holes that differ in size are formed in a color filter and a case where a pigment concentration of the color filter is changed without forming holes.
The NTSC ratio is a value representing the color purity of a color filter (the ratio in a case where the RGB (Red, Green, Blue) area in the NTSC standard is set to 100%).
This graph shows that even when the same brightness is obtained, the color purity in the case where the holes are formed is lower than that in the case where the pigment concentration is changed.
In order to improve the disadvantage of the semi-transmission type liquid crystal display device, therefore, a structure in which two color filters (a first color filter and a second color filter) of similar colors that differ in tone are formed in each of pixel regions has been proposed (see Japanese Laid-open Patent Publication No. 2001-183646).
For example, in a case where color filters are in three colors (Red, Green, and Blue), the first color filter and the second color filter that differ in tone in each of the colors are formed. That is, the structure uses color filters in a total of six colors.
That is, in the pixel region corresponding to the Red filter, a first color filter in dark red and a second color filter in light red are formed.
Similarly, a first color filter and a second color filter whose green colors differ in tone are also formed in the pixel region corresponding to the Green filter, and a first color filter and a second color filter whose blue colors differ in tone are also formed in the pixel region corresponding to the Blue filter.
A first color filter having high color purity, i.e., in a dark color (a color filter having a low light transmission factor) and a second color filter in a light color (a color filter having a high light transmission factor) are respectively arranged in a light transmission region and a light reflection region.
In the above-mentioned structure in which the color filter is provided with the holes, a high reflection factor is achieved by forming the holes in the color filter having high color purity in the light reflection region. On the other hand, the structure using the color filters in six colors is characterized in that the second color filter having a high transmission factor is formed in the light reflection region.
According to the semi-transmission type liquid crystal display device, it is possible to obtain an image quality having high color purity in the transmission mode, and it is possible to obtain an image quality having not only a high reflection factor but also high color purity in the reflection mode.
In the semi-transmission type liquid crystal display device, however, the first color filter and the second color filter are formed in the same pixel region. Therefore, when a boundary between the first color filter and the second color filter occurs in the light transmission region, the boundary may deteriorate the image quality.
That is, when a boundary 11 between the first color filter and the second color filter exists in the light transmission region, the second color filter enters a part of the light transmission region, so that the color purity in the transmission mode is reduced. Further, the white balance may be shifted.
An object of the present invention is to provide a semi-transmission type liquid crystal display device in which a first color filter and a second color filter are formed as color filters of similar colors in one pixel region, which is excellent in white balance and realizes an image quality having a high color purity in a transmission mode and an image quality having a high reflection ratio and a high color purity in a reflection mode, and display equipment using the same.